Air-conditioning method and air-conditioning system

ABSTRACT

An air-conditioning method comprises the steps of performing a refrigerator operation using a refrigerator to which cooling water cooled in a plurality of cooling towers is supplied as a cold heat source, and performing a free cooling operation using at least some of the plurality of cooling towers as a cold heat source, wherein at a time of the free cooling operation, the number of the cooling towers which are operated is controlled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air-conditioning method and anair-conditioning system, and particularly relates to an air-conditioningmethod and an air-conditioning system for a clean room, buildingair-conditioning and the like.

2. Description of the Related Art

A cooling operation is performed throughout a year in a clean room and abuilding facility. Therefore, in the air-conditioning systems of thesefacilities, energy saving is an important object. Thus, free cooling hasbeen carried out in recent years (see Japanese Patent ApplicationLaid-Open No. 2004-132651).

Free cooling refers to a system that carries out a free coolingoperation using a cooling tower as a cold heat source without using arefrigerator in winter while carrying out a refrigerator operation usingthe refrigerator as a cold heat source in summer. According to thesystem, cooling can be performed without operating the refrigerator inwinter, and therefore, a large energy saving effect can be expected.

Incidentally, such cooling systems include the case where one coolingtower is shared by both a refrigerator operation and a free coolingoperation, and the case where their own dedicated cooling towers areused in the respective operations.

SUMMARY OF THE INVENTION

However, in both cases, waste of the energy consumption amount in thecooling towers occurs. For example, in the case of sharing one coolingtower, the necessary amounts of cooling water (namely, cold heatamounts) differ in the refrigerator operation and free coolingoperation. Therefore, the cooling tower is operated in correspondencewith any one of the operations, and this becomes waste energyconsumption in the other operation.

Further, when dedicated cooling towers are used in the refrigeratoroperation and free cooling operation respectively, there arises theproblem of reducing the energy efficiency at the time of restart ofoperations.

The present invention is made in view of the above circumstances, andhas an object to provide an air-conditioning method and anair-conditioning system capable of optimizing the energy consumption ofa cooling tower.

In order to attain the above-described object, the first aspect of theinvention is an air-conditioning method for performing a refrigeratoroperation using a refrigerator to which cooling water cooled in aplurality of cooling towers is supplied as a cold heat source, and afree cooling operation using at least some of the plurality of coolingtowers as a cold heat source, and is characterized in that at a time ofthe free cooling operation, the number of the cooling towers which areoperated is controlled.

According to the present invention, by controlling the number of coolingtowers which are operated at the time of a free cooling operation, anoptimal amount of cold heat can be generated in each of the operationmodes, and the energy consumption amount as a whole can be reduced.

In the first aspect of the invention, the second aspect of the inventionis characterized in that an intermediate operation using at least someof the plurality of cooling towers as a cold heat source in combinationwith the refrigerator, and at a time of the intermediate operation, thenumber of the cooling towers which are operated to be the cold heatsource is controlled. Use of the cooling towers and the refrigerator incombination means the use of the cooling towers and the refrigerator byconnecting the cooling towers and the refrigerator in series, and refersto, for example, the case in which the cooling water cooled in thecooling tower is further cooled in the refrigerator, and supplied to theair-conditioning load part.

According to the present invention, the number of cooling towers whichare operated is also controlled at the time of the intermediateoperation, and therefore, a suitable amount of cold heat can begenerated. Thereby, the energy consumption amount as a whole can bereduced.

In the first or second aspect of the invention, the third aspect of theinvention is characterized in that switching of the operation isperformed in accordance with an outside air temperature and anair-conditioning load condition. According to the present invention, inaccordance with the outside air temperature and the air-conditioningload condition, the cold heat amount (temperature and flow rate of thecooling water) with which the energy consumption becomes the minimum canbe obtained by simulation or the like. Accordingly, by controlling thenumber of cooling towers which are operated in accordance with theresult, the air-conditioning operation in which the energy consumptionamount becomes minimum can be performed.

In any one of the first to the third aspects of the invention, thefourth aspect of the invention is characterized in that a plurality ofthe refrigerators are provided, and the number of the cooling towerswhich are operated is controlled for each of the plurality ofrefrigerators. According to the present invention, the number of coolingtowers which are operated is controlled for each of the refrigerators.Therefore, for example, when the required cold heat amount differs ineach refrigerator, the minimum required amount of cold heat can besupplied to each of the refrigerators, and the energy consumption amountas a whole can be reduced.

In any one of the first to fourth aspects of the invention, the fifthaspect of the invention is characterized in that the refrigerator is aturbo refrigerator, and inverter control is performed for therefrigerator. According to the present invention, the energy consumptionof the refrigerator can be decreased.

In any one of the first to the fifth aspects of the invention, the sixthaspect of the invention is characterized in that by controlling arotational speed of a pump which circulates the cooling water cooled inthe plurality of cooling towers or the refrigerator, a flow rate of thecooling water is controlled. According to the present invention, theenergy consumption amount required for circulation of the cooling watercan be reduced.

In order to attain the above described object, the seventh aspect of theinvention provides an air-conditioning system, characterized byincluding a plurality of cooling towers that cool cooling water, arefrigerator having a condenser and an evaporator, a circulation linefor a refrigerator operation that circulates the cooling water cooled inthe cooling tower into the condenser, and circulates the cooling watercooled in the evaporator into an air-conditioning load part, acirculation line for a free cooling operation that circulates thecooling water cooled in the cooling tower into the air-conditioning loadpart, a line switching device that switches the circulation line for therefrigerator operation and the circulation line for the free coolingoperation, and regulates the number of cooling towers to be connected tothe circulation line for the free cooling operation, and a controldevice that controls the line switching device and individually controlsoperation and stoppage of the plurality of cooling towers.

According to the present invention, the number of cooling towers whichare operated at the time of the free cooling operation can becontrolled. Accordingly, cold heat in the amount suitable for eachoperation mode can be generated, and the energy consumption amount inthe entire system can be reduced.

In the seventh aspect of the invention, the eighth aspect of theinvention is characterized by further including a circulation line foran intermediate operation that connects the plurality of cooling towersin series to the evaporator of the refrigerator, and characterized inthat the line switching device switches the lines including thecirculation line for the intermediate operation, and changes the numberof cooling towers to be connected to the circulation line for theintermediate operation.

According to the present invention, by connecting the cooling towers andthe evaporator of the refrigerator in series, the intermediate operationusing the cooling towers and the refrigerator in combination as a coldheat source can be performed. Further, according to the presentinvention, the number of cooling towers which are operated at the timeof the intermediate operation can be controlled. Therefore, the coldheat amount (the temperature and the flow rate of the cooling water) canbe regulated to the one suitable for the intermediate operation, and theenergy consumption amount of the entire system can be reduced. Thecirculation line for the intermediate operation can be also used as thefree cooling circulation line. In this case, by stopping therefrigerator, the circulation line for the intermediate operation can bealso used as the circulation line for the free cooling operation.

In the seventh or eighth aspect, the ninth aspect of the invention ischaracterized in that a plurality of the refrigerators are provided, andthe number of the cooling towers which are connected to each of therefrigerators is changed by the line switching device.

According to the present invention, the number of cooling towers whichare operated can be controlled for each of a plurality of refrigerators.Accordingly, even when the required cold heat amounts differ among aplurality of refrigerators, the cold heat amount suitable for each ofthem can be generated. Thereby, the energy consumption amount in theentire system can be reduced.

According to the present invention, by controlling the number of coolingtowers which are operated, the optimal amount of cold heat can begenerated in each of the operation modes, and the energy consumption inthe entire system can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram schematically showing the configuration of anair-conditioning system of a first embodiment;

FIGS. 2A and 2B are diagrams each schematically showing a conduitconfiguration for each operation mode;

FIG. 3 is a system diagram showing an air-conditioning system having apiping configuration differing from FIG. 1;

FIG. 4 is a system diagram showing a modified example of theair-conditioning system of FIG. 1;

FIG. 5 is a system diagram schematically showing the configuration of anair-conditioning system of a second embodiment;

FIGS. 6A to 6C are diagrams each schematically showing a conduitconfiguration for each operation mode;

FIG. 7 is a system diagram schematically showing the configuration of anair-conditioning system of a third embodiment;

FIGS. 8A and 8B are diagrams each schematically showing a conduitconfiguration for each operation mode;

FIG. 9 is a diagram schematically showing a conduit configuration foreach operation mode; and

FIG. 10 is a system diagram showing a modified example of theair-conditioning system of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of an air-conditioning method and anair-conditioning system according to the present invention will bedescribed in detail in accordance with the attached drawings.

First Embodiment

FIG. 1 is a system diagram schematically showing the configuration of anair-conditioning system of a first embodiment. An air-conditioningsystem 10 shown in the drawing is a system for carrying outair-conditioning of a clean room facility 12.

In the clean room facility 12, a fan filter unit 16 (hereinafter, FFU)is provided on a ceiling surface of a clean chamber 14, and by the FFU16, air in a ceiling space 18 is purified and is caused to flow down tothe clean chamber 14. The floor surface of the clean chamber 14 is agrating floor, the air in the clean chamber 14 is sucked into anunderfloor space 20, and further returned to the ceiling space 18through a return chamber 22. Thereby, the air in the ceiling space 18 issent to the clean chamber 14 again by the FFU 16, and the clean chamber14 is kept at high cleanliness.

A sensible heat treatment coil 24Y is provided in the return chamber 22,so as to cool the air flowing in the return chamber 22 to be able totreat sensible heat. Further, in the clean chamber 14, an apparatus 26such as a semiconductor manufacturing apparatus is provided, and a coil28 is provided in the apparatus 26 so that a refrigerant is circulatedbetween the coil 28 and an apparatus load heat exchanger 24X. Further,an external conditioner 30 is provided at the clean room facility 12.The external conditioner 30 includes an external conditioner coil 24Z, ahumidifier 32, a heater 34, a fan 36, a filter (not illustrated) and thelike, and by driving the fan 36, outside air is taken in. Subsequently,the air is subjected to dusting by a filter (not illustrated), is cooledby the external conditioner coil 24Z, is humidified by the humidifier32, is heated by the heater 34 in accordance with necessity, andthereafter, is supplied into the facility.

The air-conditioning system 10 of the present embodiment is a systemwhich supplies cold heat to the apparatus load heat exchanger 24X, thesensible heat treatment coil 24Y and the external conditioner coil 24Z,to meet a cooling load. The apparatus load heat exchanger 24X, thesensible heat treatment coil 24Y and the external conditioner coil 24Zdiffer in the temperature of the cold water which is required. Forexample, the temperatures of the cold water are set at 17° C. for theapparatus load heat exchanger 24X, at 12° C. for the sensible heattreatment coil 24Y, and at 7° C. for the external conditioner coil 24Z.Hereinafter, the apparatus load heat exchanger 24X, the sensible heattreatment coil 24Y and the external conditioner coil 24Z will be alsocalled the load part 24X, the load part 24Y and the load part 24Z.

The air-conditioning system 10 is mainly configured by eight coolingtowers 42A to 42H and three refrigerators 44X, 44Y and 44Z. The numbersof cooling towers and refrigerators are not limited to the example ofthe present embodiment, but, for example, seven cooling towers or lessor nine cooling towers or more may be adopted, and two refrigerators orless or four refrigerators or more may be adopted.

The internal construction of each of the cooling towers 42A to 42H isomitted, but each of them includes a fan for forming an ascendingcurrent of outside air in the tower, a water sprinkling pipe forsprinkling cooling water into the tower, and a water collecting unit forcollecting sprinkled cooling water. According to the cooling towers 42Ato 42H, the cooling water is sprinkled and contacts outside air, wherebythe cooling water is deprived of heat of vaporization and is cooled. Thepresent embodiment is described with the example of a closed typecooling tower, but an open type cooling tower may be used by adding aheat exchanger.

Meanwhile, three refrigerators 44X, 44Y and 44Z are devices forgenerating cooling water at temperatures necessary for the load parts24X, 24Y and 24Z respectively. Condensers 46X, 46Y and 46Z, andevaporators 48X, 48Y and 48Z are provided inside the refrigerators 44X,44Y and 44Z. The condensers 46X, 46Y and 46Z and the evaporators 48X,48Y and 48Z are connected by a circulation passage (not illustrated),and a refrigerant is circulated. The refrigerant is circulated in thecondensers 46X, 46Y and 46Z and the evaporators 48X, 48Y and 48Z,whereby the cooling water is cooled in the evaporators 48X, 48Y and 48Z.The constructions of the refrigerators 44X, 44Y and 44Z are notespecially limited, and various constructions such as a turbo type andan absorption type can be adopted, but the present embodiment isdescribed with the example of a turbo type refrigerator.

The evaporators 48X, 48Y and 48Z of the refrigerators 44X, 44Y and 44Zare connected to the load parts 24X, 24Y and 24Z. More specifically, theevaporator 48X is connected to the load part 24X through pipings x3 andx4, and a pump 50X is placed in the piping x3. By driving the pump 50X,cooling water is circulated between the evaporator 48X and the load part24X. Likewise, the evaporator 48Y is connected to the load part 24Ythrough pipings y3 and y4, and a pump 50Y is placed in the piping y3.

By driving the pump 50Y, the cooling water is circulated between theevaporator 48Y and the load part 24Y. Further, the evaporator 48Z isconnected to the load part 24Z through pipings z3 and z4, and a pump 50Zis placed in the piping z3. By driving the pump 50Z, the cooling wateris circulated between the evaporator 48Z and the load part 24Z. Thus,the refrigerators 44X, 44Y and 44Z, and the load parts 24X, 24Y and 24Zare connected one to one.

Each of the condensers 46X, 46Y and 46Z of the refrigerators 44X, 44Yand 44Z is respectively connected to the cooling towers 42A to 42H. Thecooling towers 42A to 42H are connected to the condensers 46X, 46Y and46Z in parallel. That is to say, pipings a1 to h1 for dischargingcooling water are connected to the cooling towers 42A to 42H, and thepipings a1 to h1 are connected to a main piping j1. The main piping j1branches into the pipings x1, y1 and z1, and thereafter, are connectedto the condensers 46X, 46Y and 46Z. Pipings x2, y2 and z2 fordischarging cooling water are connected to the condensers 46X, 46Y and46Z, and the pipings x2, y2 and z2 are connected to a main piping j2.The main piping j2 is branched into pipings a2 to h2, and are connectedto the water sprinkling pipes (not illustrated) of the respectivecooling towers 42A to 42H. Thereby, the cooling water which is cooled inthe respective cooling towers 42A to 42H can be circulated and suppliedto the condensers 46X, 46Y and 46Z, and the cooling towers 42A to 42Hcan be used as the cooling devices of the refrigerators 42X to 42Z.

Pumps 52 x, 52 y and 52 z are placed in the pipings x1, y1 and z1respectively, and drive control is individually performed for the pumps52 x, 52 y and 52 z, whereby the cooling water is individuallycirculated into the respective condensers 46X, 46Y and 46Z, and thecirculation amount can be regulated.

Further, three-way valves 54X, 54Y and 54Z are placed in the pipings x2,y2 and z2, and by operating the three-way valves 54X, 54Y and 54Z, partof the cooling water which flows in the pipings x2, y2 and z2 flows intothe pipings x1, y1 and z1 through bypass pipes 56X, 56Y and 56Z, so thatthe flow rate regulation is performed.

Incidentally, the cooling towers 42A to 42H are connected in series tothe evaporators 48X, 48Y and 48Z of the refrigerators 44X, 44Y and 44Z.

More specifically, the piping x3 is connected to the main piping j2through the piping x6 and is connected to the main piping j1 through thepiping x5. Accordingly, the cooling water which flows in the piping x3flows into at least one of the cooling towers 42A to 42H through thepiping x6 and the main piping j2, and returns to the original piping x3through the main piping j1 and the piping x5. Thereby, the coolingtowers 42A to 42H are connected in series to the evaporator 48X of therefrigerator 44X. A pump 58X is provided in the piping x6, and bydriving the pump 58X, the cooling water of the piping x3 flows into thepiping x6. On-off valves 60X and 62X are provided at the downstream sidedirectly from the connecting portions in the piping x3 and the pipingx6. An on-off valve 63X is provided in the piping x5. By performingopening and closing operation of the on-off valves 60X, 62X and 63X, itcan be selected whether or not to feed the cooling water in the pipingx3 to the cooling towers 42A to 42H. Further, a three-way valve 64X isplaced in the piping x6, and by operating the three-way valve 64X, partof the cooling water flowing in the piping x6 flows into the piping x5through a bypass pipe 66X, so that flow rate regulation is performed.

Likewise, the piping y3 is connected to the main piping j2 through thepiping y6, and is connected to the main piping j1 through the piping y5.Accordingly, the cooling water flowing in the piping y3 flows into atleast one of the cooling towers 42A to 42H through the piping y6 and themain piping j2, and returns to the original piping y3 through the mainpiping j1 and the piping y5. Thereby, the cooling towers 42A to 42H areconnected in series to the evaporator 48Y of the refrigerator 44Y. Apump 58Y is provided in the piping y6, and by driving the pump 58Y, thecooling water in the piping y3 flows into the piping y6. In the pipingy3 and piping y6, on-off valves 60Y and 62Y are provided at theimmediate downstream side from the connecting portions, and an on-offvalve 63Y is provided in the piping y5. By performing an opening andclosing operation of these on-off valves 60Y, 62Y and 63Y, it can beselected whether or not to feed the cooling water flowing in the pipingy3 into the cooling towers 42A to 42H. Further, a three-way valve 64Y isplaced in the piping y6, and by operating the three-way valve 64Y, partof the cooling water flowing in the piping y6 flows into the piping y5through a bypass pipe 66Y, so that the flow rate regulation isperformed.

Further, the piping z3 is connected to the main piping j2 through thepiping z6, and is connected to the main piping j1 through the piping z5.Accordingly, the cooling water flowing in the piping z3 flows into atleast one of the cooling towers 42A to 42H through the piping z6 and themain piping j2, and returns to the original piping z3 through the mainpiping j1 and the piping z5. Thereby, the cooling towers 42A to 42H areconnected in series to the evaporator 48Z of the refrigerator 44Z. Apump 58Z is provided in the piping z6, and by driving the pump 58Z, thecooling water in the piping z3 flows into the piping z6. In the pipingz3 and piping z6, on-off valves 60Z and 62Z are provided at thedownstream side directly from the connecting portions, and an on-offvalve 63Z is provided in the piping z5. By performing an opening andclosing operation of these on-off valves 60Z, 62Z and 63Z, it can beselected whether or not to feed the cooling water flowing in the pipingz3 into the cooling towers 42A to 42H. Further, a three-way valve 64Z isplaced in the piping z6, and by operating the three-way valve 64Z, partof the cooling water flowing in the piping z6 flows into the piping z5through a bypass pipe 66Z, so that flow rate regulation is performed.

As such, in the present embodiment, the cooling towers 42A to 42H can beconnected in series to the evaporators 48X, 48Y and 48Z of therefrigerators 44X, 44Y and 44Z. Thereby, the cooling towers 42A to 42Hand the refrigerators 44X, 44Y and 44Z can be used at the same time, andthe intermediate operation using the cooling towers and therefrigerators in combination as the cold heat source can be performed.Specifically, the cooling water preliminarily cooled in any of thecooling towers 42A to 42H is supplied to the refrigerators 44X, 44Y and44Z to be able to cool the refrigerators. Thereby, energy consumption ofthe refrigerators 44X, 44Y and 44Z can be decreased.

Further, according to the present embodiment, by stopping circulation ofthe refrigerant in the refrigerators 44X, 44Y and 44Z in the state inwhich the cooling towers 42A to 42H are connected in series to theevaporators 48X, 48Y and 48Z of the refrigerators 44X, 44Y and 44Z, afree cooling operation with only the cooling towers 42A to 42H as thecold heat source can be performed.

Incidentally, a plurality of on-off valves 68 for selecting the coolingtowers 42A to 42H are placed in the aforementioned main pipings j1 andj2. The on-off valves 68 are placed between the connecting portionswhere the pipings a1 to h1 are connected on the main piping j1, orplaced between the connecting portions where the pipings a2 to h2 areconnected on the main piping j2. By opening or closing any of the on-offvalves 68, the cooling towers 42A to 42H in which the cooling watercirculates can be selected. An opening and closing operation of theon-off valve 68 is performed by a control device 70.

The control device 70 is connected to a sensor 72 which measures thewet-bulb temperature of outside air, and receives the measurement dataof the outside air temperature from the sensor 72. Further, the controldevice 70 is connected to the respective load parts 24X, 24Y and 24Z,and receives the data of the load conditions from the respective loadparts 24X, 24Y and 24Z. Further, the control device 70 is connected to adrive device (not illustrated) of fans or the like of the cooling towers42A to 42H, so as to be able to control operation and stoppage of thecooling towers 42A to 42H individually. The control device 70 obtainsthe flow rate of the cooling water to be the minimum required flow rateby simulation from the outside air temperature and the data of the loadconditions, and determines the cooling towers to be operated among thecooling towers 42A to 42H so as to be able to supply the cooling watercorresponding to the flow rate. The control device 70 operates thecooling towers among the cooling towers 42A to 42H, and circulates thecooling water into the cooling towers among the cooling towers 42A to42H by controlling the on-off valve 68. Further, for the cooling towersinto which the cooling water does not have to be fed among the coolingtowers 42A to 42H, those cooling towers among the cooling towers 42A to42H are stopped.

Next, an operation method of the air-conditioning system 10 which isconfigured as described above will be described.

In summer when outside air temperature is high, a refrigerator operationusing the refrigerators 44X, 44Y and 44Z as the cold heat source isperformed. In the refrigerator operation, the on-off valves 60X, 60Y and60Z are opened, and the on-off valves 62X, 62Y, 62Z, 63X, 63Y and 63Zare closed. Thereby, a conduit construction as shown in FIG. 2A isformed. As shown in FIG. 2A, the cooling towers 42A to 42H are connectedto the condensers 46X, 46Y and 46Z of the refrigerators 44X, 44Y and44Z, and the cooling water cooled in the cooling towers 42A to 42H iscirculated and supplied to the condensers 46X, 46Y and 46Z. Further, theevaporators 48X, 48Y and 48Z of the refrigerators 44X, 44Y and 44Z andthe load parts 24X, 24Y and 24Z are connected, and the cooling watercooled in the evaporators 48X, 48Y and 48Z is supplied to the load parts24X, 24Y and 24Z. Thereby, the refrigerators 44X, 44Y and 44Z are usedas the cold heat source, and cold heat can be supplied to the load parts24X, 24Y and 24Z. In the refrigerator operation, all the cooling towers42A to 42H are used, but by performing an opening and closing operationof any of the on-off valves 68 (see FIG. 1), the number of the coolingtowers 42A to 42H to be used may be controlled. For example, by closingthe on-off valves 68 disposed in the main pipings j1 and j2 between thecooling tower 42F and the cooling tower 42G, the cooling towers 42A to42F can be used, and the number of cooling towers which are operated canbe decreased to six from eight.

Next, an intermediate operation which is performed at an outside airtemperature between summer and winter will be described. Theintermediate operation is the one using the refrigerators 44X, 44Y and44Z and some of the cooling towers 42A to 42H as a cold heat source. Theon-off valves 62X, 62Y, 62Z, 63X, 63Y and 63Z are opened and the on-offvalves 60X, 60Y and 60Z are closed. Thereby, some of the cooling towers42A to 42H and the evaporators 48X, 48Y and 48Z are connected in series.Therefore, the cooling water is preliminarily cooled in some of thecooling towers 42A to 42H first, and thereafter, is cooled in theevaporators 48X, 48Y and 48Z, and is supplied to the load parts 24X, 24Yand 24Z. Accordingly, some of the cooling towers 42A to 42H and therefrigerators 44X, 44Y and 44Z can be used in combination as the coldheat source. In the intermediate operation, remaining cooling towersamong the cooling towers 42A to 42H, and the condensers 46X, 46Y and 46Zof the refrigerators 44X, 44Y and 44Z are connected, whereby the coolingwater which is cooled in the remaining cooling towers among the coolingtowers 42A to 42H is circulated and supplied to the condensers 46X, 46Yand 46Z, and is used for cooling of the refrigerators 44X, 44Y and 44Z.

On the occasion of the intermediate operation, the number of coolingtowers 42A to 42H which are used can be controlled by opening andclosing any of the on-off valves 68 (see FIG. 1). As one example of it,FIG. 2B shows the example in which the on-off valves 68 on the mainpipings j1 and j2 are closed between the cooling tower 42F and thecooling tower 42G, between the cooling tower 42D and the cooling tower42E, and between the cooling tower 42C and the cooling tower 42D. Inthis example, the two cooling towers 42G and 42H are connected in seriesto the evaporator 48X of the refrigerator 44X, the two cooling towers42E and 42F are connected in series to the evaporator 48Y of therefrigerator 44Y, and the one cooling tower 42D is connected in seriesto the evaporator 48Z of the refrigerator 44Z. Accordingly, the numberof the cooling towers for preliminary cooling can be controlled to two,two and one. Meanwhile, the three cooling towers 42A to 42C areconnected to the condensers 46X, 46Y and 46Z of the refrigerators 44X,44Y and 44Z. Accordingly, the number of cooling towers which are used asthe cooling devices of the refrigerators 44X, 44Y and 44Z can becontrolled to three. The above description is only one example, and bychanging the positions of the on-off valves 68 which are closed, thenumber of cooling towers for preliminary cooling in each system, and thenumber of cooling towers for cooling refrigerators can be individuallycontrolled.

In winter when the outside air temperature is low, a free coolingoperation using any of the cooling towers 42A to 42H as the cold heatsource is performed. In the free cooling operation, the on-off valves62X, 62Y, 62Z, 63X, 63Y and 63Z are opened, and the on-off valves 60X,60Y and 60Z are closed. Thereby, as in the intermediate operation, anyof the cooling towers 42A to 42H is connected to the load parts 24X, 24Yand 24Z. At this time, by stopping the operation of the refrigerators44X, 44Y and 44Z, the cooling water which is cooled in the coolingtowers 42A to 42H is circulated and supplied to the load parts 24X, 24Yand 24Z, and the free cooling operation using the cooling towers 42A to42H as the cold heat source is performed. At the time of the freecooling operation, by opening and closing any of the on-off valves 68,the number of cooling towers 42A to 42H which are used can beindividually controlled in each system. Further, the systems of the loadparts 24X, 24Y and 24Z are connected to different cooling towers 42A to42H, and therefore, an optimum amount of the cooling water at an optimumtemperature can be generated for each of the systems.

The aforementioned refrigerator operation, intermediate operation andfree cooling operation are automatically switched in accordance with theoutside air temperature and the load conditions. Further, switching ofthe operation mode at this time is not limited to simultaneous switchingin all the systems of the load parts 24X, 24Y and 24Z, but may beindividually controlled in each of the systems. For example, while theintermediate operation and the free cooling operation are performed inthe systems of the load parts 24X and 24Y, the refrigerator operationmay be performed in the system of the load part 24Z. In this case, inthe system of the load part 24Z, the cooling tower for preliminarycooling and the cooling tower for free cooling are not required, andtherefore, the number of cooling towers which are used in the systems ofthe load part 24X and the load part 24Y can be increased.

For various combinations of the operation modes and the number ofcooling towers used on that occasions, various patterns are simulatedwith the outside air temperature and the load condition as the inputvalues. From the result, the minimum required cold heat amount isobtained, and in order to supply the cold heat amount, selection is madefrom the cooling towers 42A to 42H to operate the selected coolingtowers. Thereby, the energy consumption amount as an entire system canbe reduced.

As described above, according to the present embodiment, the number ofcooling towers in each of the operation modes that are the refrigeratoroperation, intermediate operation and free cooling operation can becontrolled. Therefore, by operating the minimum required number ofcooling towers 42A to 42H, energy consumption can be reduced.

In the above described embodiment, turbo refrigerators are adopted asthe refrigerators 44X, 44Y and 44Z, and can be controlled by aninverter. In this case, the energy consumption of the refrigerators 44X,44Y and 44Z can be reduced.

Further, in the above described embodiment, the rotational speeds of thepumps 50X, 50Y, 50Z, 52X, 52Y, 52Z, 58X, 58Y and 58Z can be controlledby an inverter. Thereby, the flow rate of the cooling water can becontrolled, and the energy consumption which is spent in circulation ofthe cooling water can be reduced.

The above described embodiment is the example in which the pipings areconnected so that the numbers of cooling towers for the load parts 24X,24Y and 24Z are two, two and one at the time of the intermediateoperation and the free cooling operation, but the connection of thepipings is not limited to this, and various modes can be adopted. Forexample, FIG. 3 is an example in which the number of cooling towers forthe load part 24X can be increased. In the air-conditioning system ofFIG. 3, bypass pipings 80 and 82 are provided, and one end (right end inFIG. 3) of the piping 80 is connected to the piping x6, whereas theother end (left end in FIG. 3) is branched and connected to the mainpiping j2 to be in communication with the pipings a2, b2 and c2. One end(right end in FIG. 3) of the piping 82 is connected to the piping x5,and the other end (left end in FIG. 3) is branched to be connected tothe main piping j1 so that branched portions are communicable with thepipings a1, b1 and c1. Further, the on-off valves 84 are provided in thebranched pipe portions of the piping 80 and the branched pipe portionsof the piping 82, and by opening and closing the on-off valves 84, thecooling towers 42A, 42B and 42C communicate with or are shut off fromthe load part 24X through the pipings x5 and x6. The on-off valves 84are electrically connected to the control device 70, and are subjectedto opening and closing control by the control device 70. Accordingly,the control device 70 can select whether or not to operate the coolingtowers 42A, 42B and 42C for the load part 24X.

In the air-conditioning system of FIG. 3 configured as described above,the five cooling towers 42A, 42B, 42C, 42G and 42H can be operated forthe load part 24X while the two cooling towers 42E and 42F are operatedfor the load part 24Y at the time of free cooling, and the number ofcooling towers for the load part 24X can be controlled in the range ofzero to five. Further, if the free cooling operation of the load parts24Y and 24Z is stopped, the number of cooling towers for the load part24X can be controlled in the range of zero to eight. Therefore,according to the present embodiment, the number of cooling towers forthe load part 24X can be increased, and the free cooling operation canbe performed for a long term.

FIG. 4 shows a modified example of the air-conditioning system 10 ofFIG. 1. The air-conditioning system shown in FIG. 4 has a systemconfiguration in which the intermediate operation and the free coolingoperation are not performed in the load part 24Z. Specifically, ascompared with the air-conditioning system 10 of FIG. 1, theair-conditioning system of FIG. 4 does not have the cooling tower 42D,the pipings d1, d2, z5 and z6, the on-off valves 60Z, 62Z and 63Z, thethree-way valve 64Z and the bypass pipe 66Z, and has a configuration atreduced cost. Further, the connecting position of the piping y5 and themain piping j1 and the connecting position of the piping y6 and the mainpiping j2 differ from each other.

As an operation example of the air-conditioning system of FIG. 4 asconfigured as described above, for example, in the season at a highoutside air temperature (for example, June to September), therefrigerator operation is performed in all the load parts 24X, 24Y and24Z. On this occasion, especially in the time of the year in which theoutside air temperature is high (for example, July and August), thenumber of cooling towers is controlled to six (42A, 42B, 42C, 42E, 42F,42G), and in the time of the year (for example, June and September) inwhich the outside air temperature is slightly lower than July andAugust, the number of cooling towers is controlled to five (42A, 42B,42C, 42E, 42F). Control of the number of cooling towers is performed bycontrolling the on-off valves 68 and the cooling towers 42A to 42H bythe control device 70 as in the above described air-conditioning systemof FIG. 1.

In the time of the year (for example, May and October) in which theoutside air temperature is slightly lower than that at the time of therefrigerator operation, the refrigerator operation is performed in theload parts 24Y and 24Z, whereas in the load part 24X, the operation isswitched to the free cooling operation. At this time, the three coolingtowers 42A to 42C are allowed to communicate with the condensers 46Y and46Z of the refrigerators 44Y and 44Z, and are used for the refrigeratoroperation of the load parts 24Y and 24Z. Further, the four coolingtowers 42E to 42H are used for the free cooling operation of the loadpart 24X.

At the time of the year (for example, November to April) when theoutside air temperature is low, free cooling is performed in the loadparts 24X and 24Y. At this time, the number of cooling towers can bechanged in accordance with the outside air temperature. Morespecifically, at the time of the year when the outside air temperatureis slightly high (for example, November and April), the number ofcooling towers for the load part 24Y is increased to five (42A, 42B,42C, 42E, 42F), and the number of cooling towers for the load part 24Xis reduced to two (42G, 42H). Further, at the time of the year when theoutside air temperature is low (for example, December to March), thenumber of cooling towers for the load part 24Y is decreased to four(42A, 42B, 42C, 42E), and the number of the cooling towers for the loadpart 24X is increased to three (42F, 42G, 42H).

The above described operation pattern can be determined based on theoutside air wet bulb temperature and the load conditions of the loadparts 24X to 24Z. For example, based on the outside air wet bulbtemperature and the load conditions, switch control of the number ofcooling towers can be performed by the optimization arithmetic operationof the number of cooling towers and systems with the energy consumptionamount as the evaluation function. Further, the arithmetic operationresult may be tabulated, and control may be performed.

Second Embodiment

FIG. 5 is a system diagram schematically showing the configuration of anair-conditioning system 11 of a second embodiment. The air-conditioningsystem 11 shown in FIG. 5 is the system which air-conditions the loadpart 24 of one system. The members having the same configurations andoperations as those in the first embodiment shown in FIG. 1 will beassigned with the same reference numerals and characters (X to Z areexcluded) and the description of them will be omitted.

The air-conditioning system 11 shown in FIG. 5 includes one refrigerator44 and three cooling towers 42A to 42C. A condenser 46 of therefrigerator 44 is connected to each of the cooling towers 42A to 42C,and the cooling towers 42A to 42C are connected in parallel to thecondenser 46. Specifically, the pipings a1 to c1 for draining thecooling water are connected to the cooling towers 42A to 42C, and afterthe pipings a1 to c1 are connected to the main piping j1, the mainpiping j1 is connected to the condenser 46. The main piping j2 connectedto the condenser 46 is branched into the pipings a2 to c2 for inflow ofthe cooling water, and the pipings a2 to c2 are connected to therespective cooling towers 42A to 42C. A pump 52 is placed in the mainpiping j1, and by driving the pump 52, the cooling water circulatesbetween the cooling towers 42A to 42C and the condenser 46, and thecirculation amount of the cooling water is regulated. Further, athree-way valve 54 is provided in the main piping j2 to allow part ofthe cooling water flowing in the main piping j2 into the main piping j1through a bypass piping 56 so that the flow rate regulation can beperformed.

An evaporator 48 of the refrigerator 44 is connected to the load part 24through pipings k3 and k4. The pump 52 is connected to the piping k3.Thereby, the cooling water cooled in the evaporator 48 can be circulatedand supplied to the load part 24.

The cooling towers 42A to 42C are connected in series to the evaporator48. Specifically, the piping k3 is connected to the main piping j2through the piping k6, and is connected to the main piping j1 throughthe piping k5. Accordingly, the cooling water which flows in the pipingk3 flows into at least one of the cooling towers 42A to 42C through thepiping k6 and the main piping j2, and returns to the original piping k3through the main piping j1 and the piping k5. Thereby, the coolingtowers 42A to 42C are connected in series to the evaporator 48 of therefrigerator 44. A pump 58 is provided in the piping k6, and by drivingthe pump 58, the cooling water in the piping k3 flows into the pipingk6. Further, in the piping k3 and the piping k6, on-off valves 60 and 62are provided at the immediate downstream side from the connectingportions. Further, an on-off valve 63 is provided in the piping k5. Byperforming opening and closing operation of these on-off valves 60, 62and 63, it can be selected whether or not to feed the cooling water inthe piping k3 to the cooling towers 42A to 42C. Further, a three-wayvalve 64 is placed in the piping k6, and by operating the three-wayvalve 64, part of the cooling water which flows in the piping k6 flowsinto the piping k5 through the bypass pipe 66, and flow rate regulationis performed.

In the above described main pipings j1 and j2, a plurality of on-offvalves 68 for selecting the cooling towers 42A to 42C are placed. Theon-off valves 68 are placed between the connecting portions where thepipings a1 to c1 are connected on the main piping j1, or between theconnecting portions where the pipings a2 to c2 are connected on the mainpiping j2. By opening and closing any of the on-off valves 68, selectioncan be made from the cooling towers 42A to 42C in which the coolingwater is circulated. The opening and closing operation of the on-offvalve 68 is performed by the control device 70.

The control device 70 is connected to the sensor 72 for measuring anoutside air wet-bulb temperature, and receives the measurement data ofthe outside air temperature from the sensor 72. Further, the controldevice 70 is connected to the load part 24, and receives the data of theload condition from the load part 24. Further, the control device 70 isconnected to a drive device (not illustrated) of fans or the like of thecooling towers 42A to 42C, and can control operation and stoppage of thecooling towers 42A to 42C. The control device 70 obtains the minimumrequired flow rate of the cooling water by simulation from the outsideair temperature and the data of the load condition, and determines thecooling towers to be operated among the cooling towers 42A to 42C so asto be able to supply the cooling water at the corresponding flow rate.The control device 70 operates the cooling towers among the coolingtowers 42A to 42C, and controls the on-off valves 68 to circulate thecooling water into the cooling towers among the cooling towers 42A to42C. For the cooling towers into which the cooling water does not needto be fed among the cooling towers 42A to 42C, such cooling towers amongthe cooling towers 42A to 42C are stopped.

Next, an operation method of the air-conditioning system 11 configuredas described above will be described.

In summer when the outside air temperature is high, a refrigeratoroperation using the refrigerator 44 as the cold heat source isperformed. In the refrigerator operation, the on-off valve 60 is opened,and the on-off valves 62 and 63 are closed. Thereby, a conduitconfiguration as shown in FIG. 6A is formed. As shown in FIG. 6A, thecooling towers 42A to 42C are connected to the condenser 46 of therefrigerators 44, and the cooling water cooled in the cooling towers 42Ato 42C is circulated and supplied to the condenser 46. Further, theevaporator 48 of the refrigerator 44 and the load part 24 are connected,and the cooling water cooled in the evaporators 48 is supplied to theload part 24. Thereby, the refrigerator 44 is used as the cold heatsource, and cold heat can be supplied to the load part 24. At this time,by opening and closing any of the on-off valves 68, the number ofcooling towers to be used of the cooling towers 42A to 42C can becontrolled.

In an intermediate operation, the on-off valves 62 and 63 are opened,and the on-off valve 60 is closed. Thereby, some of the cooling towers42A to 42C and the evaporator 48 are connected in series. Therefore, thecooling water is preliminarily cooled in some of the cooling towers 42Ato 42C first, and thereafter, is cooled in the evaporator 48, and issupplied to the load part 24. Accordingly, some of the cooling towers42A to 42C and the refrigerator 44 can be used in combination as thecold heat source. In the intermediate operation, remaining coolingtowers of the cooling towers 42A to 42C and the condenser 46 of therefrigerator 44 are connected, whereby the cooling water which is cooledin the remaining cooling towers of the cooling towers 42A to 42C iscirculated and supplied to the condenser 46, and is used for cooling ofthe refrigerator 44. At the time of the intermediate operation, thenumber of cooling towers 42A to 42C which are used can be controlled byopening and closing any of the on-off valves 68. As one example of it,FIG. 6B shows the example in which the on-off valves 68 are closedbetween the cooling tower 42A and the cooling tower 42B, and between thecooling tower 42B and the cooling tower 42C. In this example, the onecooling tower 42C is connected in series to the evaporator 48 of therefrigerator 44, and therefore, the number of the cooling towers forpreliminary cooling is one. Further, the one cooling tower 42A isconnected to the condenser 46 of the refrigerator 44, and therefore, thenumber of cooling towers to be used as the cooling device for therefrigerator 44 is controlled to one. The above description is oneexample, and by changing the positions of the on-off valves 68 to beclosed, the number of cooling towers for preliminary cooling and thenumber of cooling towers for cooling the refrigerator can beindividually controlled.

In winter when the outside air temperature is low, a free coolingoperation using any of the cooling towers 42A to 42C as the cold heatsource is performed. In the free cooling operation, the on-off valves 60are closed. Thereby, as in the intermediate operation, the coolingtowers 42A to 42C are connected to the load part 24. At this time, theoperation of the refrigerator 44 is stopped. Accordingly, the coolingwater which is cooled in the cooling towers 42A to 42C is circulated andsupplied to the load part 24, and the free cooling operation with thecooling towers 42A to 42C as the cold heat source is performed. At thetime of the free cooling operation, by opening and closing any of theon-off valves 68, the number of cooling towers 42A to 42C to be used canbe controlled. For example, as in FIG. 6C, the two cooling towers 42Band 42C can be used for a free cooling operation.

As described above, according to the present embodiment, the number ofcooling towers in each of the operation modes that are the refrigeratoroperation, intermediate operation and free cooling operation can becontrolled. Therefore, by operating the minimum required number ofcooling towers 42A to 42C, energy consumption can be reduced.

In the above described first and second embodiments, the number ofcooling towers which are operated is controlled, but while all thecooling towers are being operated, the numbers of cooling towersassigned to the circulation destinations of the cooling water may bechanged.

Third Embodiment

FIG. 7 is a system configuration schematically showing the configurationof an air-conditioning system 10 of a third embodiment. Theair-conditioning system 10 shown in FIG. 7 is the system whichair-conditions the load part 24 of one system. The members having thesame configurations and operations as those in the first embodimentshown in FIG. 1 will be assigned with the same reference numerals andcharacters and the description of them will be omitted in some cases.

As compared with the first embodiment, besides the number of coolingtowers and refrigerators, the cooling towers are open type coolingtowers including heat exchangers and the load part is of one system inthe third embodiment.

The air-conditioning system 10 shown in FIG. 7 includes tworefrigerators 44X and 44Y, five cooling towers 42A to 42E, and heatexchangers 80X and 80Y for free cooling which are connected to thecooling towers 42A to 42E. In the present embodiment, the cooling towers42A to 42E are configured by open type cooling towers. An open typecooling tower includes a water sprinkling pipe for sprinkling coolingwater, and a water collecting pipe for collecting the sprinkled coolingwater, and the cooling water is sprinkled from the water sprinkling pipeto be in contact with outside air, and thereby deprived of heat ofvaporization to be cooled. When open type cooling towers are adopted asthe cooling towers 42A to 42E, in the operation in the refrigerators 44Xand 44Y, the cooling water temperature of the refrigerators 44X and 44Ybecomes low as compared with the case of adopting closed type coolingtowers, the coefficients of performance of the refrigerators 44X and 44Yare improved, and energy saving is realized. Further, the open typecooling tower can make the installation area smaller as compared withthe closed type cooling tower, and cost can be reduced.

The connection relation of the heat exchangers 80X and 80Y, the coolingtowers 42A to 42E and the load part 24 will be described. The pipings a1to e1 for draining the cooling water are connected to the cooling towers42A to 42E, and the pipings a1 to e1 are connected to the main pipingj1. After the main piping j1 is branched into pipings x5 and y5, theyare connected to the heat exchangers 80X and 80Y.

The pipings x6 and y6 for draining the cooling water are connected tothe heat exchangers 80X and 80Y, and the pipings x6 and y6 are connectedto the main piping j2. The main piping j2 is branched into the pipingsa2 to e2, which are connected to water sprinkling pipes (notillustrated) of the respective cooling towers 42A to 42E. Pumps 59 x and59 y are placed in the pipings x5 and y5. By performing drive control ofthe pumps 59 x and 59 individually, the cooling water is individuallycirculated between each of the heat exchangers 80X and 80Y and thecooling towers 42A to 42E.

Pipings x7 and x8 are connected to the heat exchanger 80X. The piping x7is connected to the piping x3, and the piping x8 is connected to thepipings x3 and x4. Further, pipings y7 and y8 are connected to the heatexchanger 80Y. The piping y7 is connected to the piping y3, and thepiping y8 is connected to the piping y4. The heat exchanger 80X isconnected to the load part 24 through the pipings x3, x4, x7 and x8. Theheat exchanger 80Y is connected to the load part 24 through the pipingsy3, y4, y7 and y8.

The pump 58X is placed in the piping x7, and the pump 58Y is placed inthe piping y7. By driving the pump 58X, the cold water can be circulatedbetween the heat exchanger 80X and the load part 24. Similarly, bydriving the pump 58Y, the cooling water can be circulated between theheat exchanger 80Y and the load part 24.

The on-off valve 60X is provided in the piping x3, the on-off valve 62Xis provided in the piping x7, and the on-off valve 63X is provided inthe piping x8. By performing an opening and closing operation of theseon-off valves 60X, 62X and 63X, it can be selected whether to feed thecold water in the pipings x3 and x4 to the heat exchanger 80X or to therefrigerator 44X.

Similarly, the on-off valve 60Y is provided in the piping y3, the on-offvalve 62Y is provided in the piping y7, and the on-off valve 63Y isprovided in the piping y8. By performing opening and closing operationof these on-off valves 60Y, 62Y and 63Y, it is selected whether to feedthe cold water in the pipings y3 and y4 to the heat exchanger 80 y or tothe refrigerator 44Y.

Next, the connection relation of the refrigerators 44X and 44Y, thecooling towers 42A to 42E and the load part 24 will be described. Therefrigerators 44X and 44Y includes therein the condensers 46X and 46Y,and the evaporators 48X and 48Y. The evaporator 48X is connected to theload part 24 through the pipings x3 and x4. Further, the evaporator 48Yis connected to the load part 24 through the pipings y3 and y4.

The condensers 46X and 46Y of the refrigerators 44X and 44Y arerespectively connected to the cooling towers 42A to 42E. The coolingtowers 42A to 42E are connected in parallel to the condensers 46X and46Y. The pipings a1 to e1 for draining the cooling water are connectedto the cooling towers 42A to 42E, and the pipings a1 to e1 are connectedto the main piping j1. After the main piping j1 is branched into thepipings x1 and y1, they are connected to the respective condensers 46Xand 46Y. The pipings x2 and y2 for draining the cooling water areconnected to the condensers 46X and 46Y, and the pipings x2 and y2 areconnected to the main piping j2. The main piping j2 is branched into thepipings a2 to e2, and they are connected to the water sprinkling pipes(not illustrated) of the respective cooling towers 42A to 42E. Thereby,the cooling water cooled in the respective cooling towers 42A to 42E canbe circulated and supplied to the condensers 46X and 46Y, and thecooling towers 42A to 42E can be used as the cooling device for therefrigerators 42X and 44Y.

The pumps 52 x and 52 y are placed in the pipings x1 and y1. Byperforming drive control of the pumps 52 x and 52 y individually, thecooling water is circulated into the respective condensers 46X and 46Yindividually, and the circulation amount of it is regulated.

The evaporator 48X of the refrigerator 44X is connected to the load part24 through the pipings x3 and x4. The pump 50X is placed in the pipingx3, and by driving the pump 50X, the cold water is circulated betweenthe evaporator 48X and the load part 24. Similarly, the evaporator 48Yof the refrigerator 44Y is connected to the load part 24 through thepipings y3 and y4. The pump 50Y is placed in the piping y3, and bydriving the pump 50Y, the cold water is circulated between theevaporator 48Y and the load part 24.

The pipings a1 to e1 are connected to the main piping j1, the pipings a2to e2 are connected to the main piping j2, and the aforementionedcooling towers 42A to 42E are connected in parallel to the refrigerators44X and 44Y. Similarly, the cooling towers 42A to 42E are connected inparallel to the heat exchangers 80X and 80Y. In the present embodiment,the main pipings j1 and j2 form a common circulation passage of thecooling water with respect to the heat exchangers 80X and 80Y and therefrigerators 44X and 44Y.

A plurality of on-off valves 68 for selecting the cooling towers 42A to42E are placed in the aforementioned main pipings j1 and j2. The on-offvalves 68 are placed between the connecting portions where the pipingsa1 to e1 are connected on the main piping j1, or are placed between theconnecting portions where the pipings a2 to e2 are connected on the mainpiping j2. By opening and closing any of the on-off valves 68, thecooling towers 42A to 42E to which the cooling water is circulated canbe selected. The opening and closing operation of the on-off valve 68 isperformed by the control device 70.

The control device 70 is connected to the sensor 72 for measuring theoutside air wet bulb temperature, and receives the measurement data ofthe outside air temperature from the sensor 72. Further, the controldevice 70 is connected to the load part 24, and receives the data of theload conditions from the load part 24. Further, the control device 70 isconnected to the drive device (not illustrated) of the fans or the likeof the cooling towers 42A to 42E, so as to be able to control operationand stoppage of the cooling towers 42A to 42E. The control device 70determines the cooling towers to be operated among the cooling towers42A to 42E by the simulation from the outside air temperature and thedata of the load condition. Subsequently, the control device 70 operatesthe cooling towers among the cooling towers 42A to 42E, and controls theon-off valve 68 to circulate the cooling water to the cooling towersamong the cooling towers 42A to 42E. Further, for the cooling towersinto which the cooling water does not have to be fed among the coolingtowers 42A to 42E, the control device 70 stops such cooling towers amongthe cooling towers 42A to 42E.

Further, by the control device 70, each of the inverters provided in thefans of the cooling towers 42A to 42E, the pumps 50X, 50Y, 52X, 52Y,58X, 58Y, 59X and 59Y is controlled, and is driven so that the totalpower consumption of the refrigerators, fans and pumps becomes theminimum value.

The control is performed as follows as an example. First, the outsideair wet bulb temperature, the load, the cooling water temperatures atthe outlets of the cooling towers 42A to 42E, and the cold watertemperatures at the outlets of the heat exchangers 80X and 80Y are usedas input values, and the input value data are input to the simulatorwhich performs simulation for obtaining the total value of the powerconsumption of the fans of the cooling towers 42A to 42E, and the pumps50X, 50Y, 52X, 52Y, 58X, 58Y, 59X, 59Y and the like. At this time, theinput value data are input to the simulator while the input values ofthe cooling water temperatures and the cold water temperature arechanged. From the simulation result, the frequencies (rotational speeds)of the fans of the cooling towers 42A to 42E and the pumps 50X, 50Y,52X, 52Y, 58X, 58Y, 59X and 59Y at which the total value of the powerconsumption becomes minimum are obtained as the optimal values. By thecontrol device 70, the actual cooling water temperature and the coldwater temperature are set to the obtained optimal values. By the controldevice 70, the inverters of the cooling water pumps (52X, 52Y, 59X, 59Y)and the cold water pumps (50X, 50Y) are controlled to correspond to thechange of the outside air wet bulb temperature state and the coolingload amount to change the flow rate, and energy saving is realized.

In the system operating the refrigerators, by using the simulator forperforming simulation for obtaining the total value of the powerconsumption of the refrigerator, cooling tower, cooling water pump andcold water pump, the cooling water pump frequency, the cooling watertemperature and the cold water temperature at which the total value ofthe power consumption becomes minimum are obtained, and the coolingtower fans and pumps are controlled.

Next, an operation method of the air-conditioning system 10 configuredas described above will be described. In summer when the outside airtemperature is high, the refrigerator operation using the refrigerators44X and 44Y as the cold heat source is carried out. In the refrigeratoroperation, the on-off valves 60X and 60Y are opened, and the on-offvalves 62X, 62Y, 63X and 63Y are closed. Thereby, the conduitconfiguration as shown in FIG. 8A is formed. As shown in FIG. 8A, thecooling towers 42A to 42E are connected to the condensers 46X and 46Y ofthe refrigerators 44X and 44Y. By driving the pumps 52X and 52Y, thecooling water cooled in the cooling towers 42A to 42E is circulated andsupplied to the condensers 46X and 46Y. The evaporators 48X and 48Y ofthe refrigerators 44X and 44Y and the load part 24 are connected. Bydriving the pumps 50X and 50Y, the cold water cooled in the evaporators48X and 48Y is supplied to the load part 24. Therefore, cold heat can besupplied to the load part 24 with the refrigerators 44X and 44Y as thecold heat source. At this time, by opening and closing operation of anyof the on-off valves 68, the number of cooling towers 42A to 42E to beused can be also controlled.

In winter when the outside air temperature is low, a free coolingoperation using any of the cooling towers 42A to 42E as the cold heatsource is performed. In the free cooling operation, the pumps 50X and50Y are stopped, the on-off valves 60X and 60Y are closed, and theon-off valves 62X, 62Y, 63X and 63Y are opened. The pressure loss of theon-off valves 63X and 63Y is smaller than the pressure loss of the pumps50X and 50Y. Therefore, the cold water from the heat exchangers 80X and80Y flows in the pipings x8 and y8, and flows into the load part 24through the on-off valves 63X and 63Y. Thereby, the cooling towers 42Ato 42E are connected to the heat exchangers 80X and 80Y, and the heatexchangers 80X and 80Y are connected to the load part 24. At this time,operation of the refrigerators 44X and 44Y is stopped. By driving thepumps 59X and 59Y, the cooling water cooled in the cooling towers 42A to42E is circulated and supplied to the heat exchangers 80X and 80Y. Bydriving the pumps 58X and 58Y, the cold water cooled in the heatexchangers 80X and 80Y is supplied to the load part 24. At the time of afree cooling operation, by opening and closing any of the on-off valves68, the number of cooling towers 42A to 42E to be used can becontrolled. For example, in FIG. 8B, the three cooling towers 42C to 42Ecan be used for the free cooling operation.

Next, the intermediate operation which is performed at the time of theoutside air temperature between summer and winter will be described withreference to FIG. 9. In the intermediate operation, the cooling towersare switched to the refrigerator side and the heat exchanger side forfree cooling. Specifically, the operation using the refrigerators 44Xand 44Y and some of the cooling towers 42A to 42E as the cold heatsource is performed. The on-off valve 68 at the inlet side and theon-off valve 68 at the outlet side between the cooling towers 42B and42C are closed. In accordance with the outside air temperature and theload condition, the on-off valve 68 between the cooling towers 42A and42B and the on-off valve 68 between the cooling towers 42C and 42D areswitched to closing. The on-off valves 60X, 63X, 60Y and 63Y are closed,and the on-off valves 62X and 62Y are opened. Thereby, the passage forfeeding water to the refrigerator is formed in the rear stage of theheat exchanger for free cooling. Specifically, the cold water flows inthe pipings x3 and x7, the heat exchanger 80X, and the pipings x8, x3and x4, and is circulated and supplied to the evaporator 48X as shown bythe arrows. Similarly, the cold water flows in the pipings y3 and y7,the heat exchanger 80 y, and the pipings y8, y3 and y4, and iscirculated and supplied to the evaporator 48 y as shown by the arrows.

As such, according to the present embodiment, the number of coolingtowers in each of the operation modes of the refrigerator operation,intermediate operation and free cooling operation can be controlled.Therefore, by operating the minimum required number of cooling towersamong the cooling towers 42A to 42E, energy consumption amount can bereduced.

Further, the piping system including the on-off valves 63X and 63Y iseliminated, that is, the piping for connecting the piping x3 and thepiping x4, and the piping for connecting the piping y3 and y4 areeliminated, and at the time of a free cooling operation, cold water isfed to the refrigerators in the case of the intermediate operation as inFIG. 6 to cope with the cases of the refrigerator operation, theintermediate operation and the free cooling operation.

FIG. 10 shows a modified example of the air-conditioning system 10 ofFIG. 7. The air-cooling system shown in FIG. 10 has a piping systemwhich can switch the cooling water system for feeding the water for eachcooling tower.

As shown in FIG. 10, the main piping j1 is connected to therefrigerators 44X and 44Y through the pipings x2 and y2. The main pipingj2 is connected to the refrigerators 44X and 44Y through the pipings x1and y1. The pipings a1 to e1 are connected to the main piping j1, andthe cooling towers 42A to 42E and the main piping j1 are connectedthrough the pipings a1 to e1. The on-off valve 68 is provided at each ofthe pipings a1 to e1. The pipings a2 to e2 are connected to the mainpiping j2, and the cooling towers 42A to 42E and the main piping j2 areconnected through the pipings a2 to e2. The on-off valve 68 is providedin each of the pipings a2 to e2.

Meanwhile, a main piping j3 is connected to the heat exchangers 80X and80Y through the pipings x5 and y5. Further, a main piping j4 isconnected to the heat exchangers 80X and 80Y through the pipings x6 andy6. Pipings a3 to e3 are connected to the main piping j3, and thecooling towers 42A to 42E and the main piping j3 are connected throughthe pipings a3 to e3. The on-off valve 68 is provided at each of thepipings a3 to e3. Pipings a4 to e4 are connected to the main piping j4,and the cooling towers 42A to 42E and the main piping j4 are connectedthrough the pipings a4 to e4. The on-off valve 68 is provided at each ofthe pipings a4 to e4.

In the present embodiment, the circulation passage is formed between therefrigerators 44X and 44Y and the cooling towers 42A to 42E by the mainpipings j1 and j2, and a circulation passage is formed between the heatexchangers 80X and 80Y and the cooling towers 42A to 42E by the mainpipings j3 and j4.

By opening and closing any of a plurality of on-off valves 68 providedin the pipings a1 to e1, a2 to e2, a3 to e3 and a4 to e4, any of therefrigerators 44X and 44Y and the heat exchangers 80X and 80Y for freecooling can be selected for the cooling water for each of the coolingtowers 42A to 42E.

By adopting such a configuration, the number of on-off valves where thecooling water passes when the cooling water is fed to the pipings can bereduced. Thereby, the piping resistance becomes low, and the power ofthe pump can be reduced. In the present embodiment, by feeding thecooling water through only one on-off valve 68, the cooling water fromthe cooling towers 42A to 42E can be fed to the main piping j1 or j3.

Meanwhile, in the configuration shown in FIG. 7, the number of on-offvalves to the heat exchanger is large in the cooling towers far from theheat exchanger, and the piping resistance is large. For example, thecooling water in the cooling tower 42A passes through a plurality ofon-off valves 68 and is fed to the heat exchangers 80X and 80Y.

Further, in the air-conditioning system 10 shown in FIG. 10, water canbe fed irrespective of the sequence from the heat exchangers and therefrigerators.

Accordingly, the degree of freedom of selection of the cooling tower tobe switched to the heat exchanger system and the refrigerator systembecomes high. The systems of the inlet and outlet of the cooling towermay be realized by the branched pipes.

1. An air-conditioning method comprising the steps of: performing arefrigerator operation using a refrigerator to which cooling watercooled in a plurality of cooling towers is supplied as a cold heatsource, and performing a free cooling operation using at least some ofthe plurality of cooling towers as a cold heat source, wherein at a timeof the free cooling operation, the number of the cooling towers whichare operated is controlled.
 2. The air-conditioning method according toclaim 1, wherein an intermediate operation which uses at least some ofthe plurality of cooling towers as a cold heat source in combinationwith the refrigerator is performed, and at a time of the intermediateoperation, the number of the cooling towers which are operated to be thecold heat source is controlled.
 3. The air-conditioning method accordingto claim 1, wherein switching of the operation is performed inaccordance with an outside air temperature and an air-conditioning loadcondition.
 4. The air-conditioning method according to claim 1, whereina plurality of the refrigerators are provided, and the number of thecooling towers which are operated is controlled for each of theplurality of refrigerators.
 5. The air-conditioning method according toclaim 1, wherein the refrigerator is a turbo refrigerator, and invertercontrol is performed for the refrigerator.
 6. The air-conditioningmethod according to claim 1, wherein by controlling a rotational speedof a pump which circulates the cooling water cooled in the plurality ofcooling towers or the refrigerator, a flow rate of the cooling water iscontrolled.
 7. An air-conditioning system, comprising: a plurality ofcooling towers that cool cooling water; a refrigerator having acondenser and an evaporator; a circulation line for a refrigeratoroperation that circulates the cooling water cooled in the cooling towerinto the condenser, and circulates the cooling water cooled in theevaporator into an air-conditioning load part; a circulation line for afree cooling operation that circulates the cooling water cooled in thecooling tower into the air-conditioning load part; a line switchingdevice that switches the circulation line for the refrigerator operationand the circulation line for the free cooling operation, and regulatesthe number of cooling towers to be connected to the circulation line forthe free cooling operation; and a control device that controls the lineswitching device and individually controls operation and stoppage of theplurality of cooling towers.
 8. The air-conditioning system according toclaim 7, further comprising a circulation line for an intermediateoperation that connects the plurality of cooling towers in series to theevaporator of the refrigerator, wherein the line switching deviceswitches the lines including the circulation line for the intermediateoperation, and changes the number of cooling towers to be connected tothe circulation line for the intermediate operation.
 9. Theair-conditioning system according to claim 7, wherein a plurality of therefrigerators are provided, and the number of the cooling towers whichare connected to each of the refrigerators is changed by the lineswitching device.